1. Field of the Invention
The present invention relates to a light valve projection apparatus for magnified projection of an image of a liquid crystal panel or a micromirror rocking pixel panel, and more particularly to a projection apparatus equipped, as the light source, with a light source of instantly light emitting type and that of high efficiency and high color presenting ability. The present invention is applicable to a projector of front projection type for direct projection onto a reflective screen, a projection of rear projection type for projection on a transmissive screen, or an apparatus in which either of the foregoing is combined with another equipment, utilizing a transmissive or reflective liquid crystal device or a micro mirror rocking pixel device.
2. Related Background Art
There are already commercialized apparatus for magnified projection of the image of a light valve panel such as a liquid crystal device, utilizing a light source such as a metal halide lamp.
In such apparatus the light emitted from the light source is concentrated on a light valve panel for example through a mirror, and is projected through a projection lens onto a screen.
The apparatus is known in various types such as a single panel type utilizing a liquid crystal panel, and a three-panel type in which three liquid crystal panels are illuminated by color separation through dichroic mirrors and the transmitted lights are color synthesized, and the liquid crystal panel of transmissive type is adopted for this purpose but that of reflective type is also utilized recently.
Also instead of the liquid crystal panel, there has been developed a panel in which micromirrors are arrayed on a semiconductor chip as pixels and the micromirror of each pixel is driven in a rocking motion to control the gradation, and such panel is also utilized in a single panel type utilizing color-sequential light sources and a three-panel type in which three panels are illuminated by color separation through dichroic mirrors and the reflected lights are color synthesized.
The illumination for such projector is required to be of a high illumination intensity in order that the projected image can be viewed on a large screen even in a well lighted room, and, for this reason, the light source is principally composed of a metal halide lamp or a high pressure mercury lamp of high efficiency and high color presenting ability.
FIG. 11 shows an example of the configuration of a conventional liquid crystal projector of three panel type.
In FIG. 11, there are shown a metal halide lamp la which is a discharge tube, a reflector 1b formed in an elliptic or parabolic surface, an electrode 1c of the metal halide lamp 1a, a first fly""s eye lens 7, dichroic mirrors 8, 9, mirrors 10, 11, 12, a cross dichroic prism 13, a projection lens 14, a red-color transmissive liquid crystal panel 15, a green-color transmissive liquid crystal panel 16, a blue-color transmissive liquid crystal panel 17, an optical system shielding case 18, and an external casing 100 containing the entire projection system.
When a power switch of the apparatus shown in FIG. 11 is turned on, the metal halide lamp 1a is energized and starts lighting.
Then the light emitted from the metal halide lamp 1a is converted into a relatively parallel illuminating light by the reflector 1b and enters the fly""s eye lens 5.
The fly""s eye lens 5 has a composite structure of plural lenses and has an effect, in combination with a fly""s eye lens 7, of flattening the luminance on an irradiated surface at the rear.
A mirror 6 bends the optical path of the illuminating light from the fly""s eye lens 5 by 90xc2x0 for entry into the fly""s eye lens 7.
The mirror 6 is provided with a dichroic film for transmitting infrared and ultraviolet light, thereby reducing the infrared and ultraviolet components in the visible light entering the fly"" eye lens 7 and thus reducing heat generation and improving reliability.
The visible light emerging from the fly""s eye lens 7 enters a dichroic mirror 8 through which blue light is transmitted, then bent in the optical path by a mirror 10 and enters a transmissive liquid crystal panel 17 for blue color.
On the other hand, in the dichroic mirror 8, the light of green and red colors, having a wavelength longer than that of blue color, is reflected and enters a dichroic mirror 9.
The dichroic mirror 9 has a property of reflecting green light and illuminates a transmissive liquid crystal panel 16 for green color.
In the dichroic mirror 9, the light red color, having a wavelength longer than that of the green color, is reflected, then bent in the optical path by mirrors 11, 12 and illuminates a transmissive liquid crystal panel 15 for red color.
The aforementioned liquid crystal panels 15, 16, 17 respectively for red, green and blue colors receive unrepresented drive signals for the respective colors to display an image in the display area of each panel, thereby optically modulating the illuminating light mentioned above.
The image displayed on the green liquid crystal panel 16 is being vertically inverted (FIG. 11 being a plan view) electrically or by reversing the front and back surfaces of the panel with respect to the images displayed on the liquid crystal panels 15, 17 for other colors, in consideration of the process of image synthesis in a dichroic mirror 13.
The image lights from the transmissive liquid crystal panels 15, 16, 17 for the red, green and blue colors enter a cross dichroic prism 13 respectively from predetermined directions as illustrated, thus being synthesized and emerging as a color image from an illustrated fourth face and enters a projection lens 14 for magnified projection onto a screen.
Also a configuration employing two light sources is disclosed in the Japanese Utility Model Application Laid-open No. 4-33034 and the Japanese Patent Application Laid-open No. 9-127467.
An object of the present invention is to provide a preferred configuration employing plural light sources in a projection apparatus.
If the light source of a projection apparatus of liquid crystal panel type or micromirror rocking pixel panel type is composed of a discharge lamp of high efficiency and high color presenting ability such as a metal halide lamp or a high pressure mercury lamp, there is required a time of at least 2 to 3 minutes until such illuminating lamp reaches a predetermined light amount after the power supply is turned on.
Also in case of recovery from an instantaneous interruption of the power supply for certain reason, there is required an even longer time (3 to 5 minutes) before the lamp can be turned on again. Thus, there is encountered a serious drawback that the image cannot be projected during such period, particularly in applications requiring urgency, such as important presentations or conferences.
In such situation, the presence of plural light sources may be advantageous for illuminating the light valve. The present invention is to provide, in case of employing plural light sources, a configuration capable of efficiently illuminating the light valve or a configuration enabling simplification even in case of using plural light sources.
According to one of the inventions of the present application, there is provided a projection apparatus provided with a light valve which modulates light by two-dimensionally arranged plural pixels and projects thus modulated light, the apparatus comprising:
a first light source;
a second light source;
a mirror for guiding the light from the first light source or the light from the second light source; and
a movable mechanism for varying the relative position between the mirror and the first and second light sources.
In such configuration, owing to the presence of the movable mechanism for changing the relative position between the mirror and the light sources, there can be switched a state in which the first light source principally irradiates the light valve and a state in which the second light source principally irradiates the light valve by varying the relative position between the mirror and the light sources.
In this manner there can be dispensed with a half mirror to be provided on the optical paths of the output lights from the separately provided light sources for using such optical paths partly in common.
For varying the relative position between the mirror and the light sources, there can be advantageously employed a configuration for moving the position of the mirror or a configuration for moving the position of the light sources.
According to another of the inventions of the present application, there is provided a projection apparatus provided with a light valve which modulates light by two-dimensionally arranged plural pixels and projects thus modulated light, the apparatus comprising:
a first light source;
a second light source; and
a reflector for condensing the light from the first light source and the light from the second light source;
wherein the first and second light sources are positioned in the vicinity of the focal point of the reflector.
This invention allows to extremely simplify the structure of the light source portion, and there can be advantageously employed a configuration in which the first light source and the second light source have different light emitting characteristics (particularly change in the light amount with the lapse of time after the power supply is turned on).
Also in this invention, there can be employed a configuration in which the first light source includes light regulating means for regulating the light amount irradiating the light valve. For such light regulating means, there can be advantageously employed a control circuit for regulating the amount of the output light of the first light source.
There is also advantageously employed a configuration in which the light amount of the first light source irradiating the light valve is gradually decreased within a period after the power supply to the second light source is turned on and until the second light source reaches the stably turned-on state.
There can be reduced the unpleasant feeling on the observed image by such control that the sum of the light amount irradiating the light valve by the first light source and that irradiating the light valve by the second light source approaches a constant value. For such control, there can be employed a control circuit for regulating the amount of the output light of the first light source.
For realizing such light regulation, there can be adopted a configuration for regulating the light according to correction data, based on the change of the light amount of the second light source as a function of the lapse of time from the start of light emission. The light regulation in such case can be realized with the lapse of time. A timer may be used for realizing the light regulation according to the lapse of time. Also there may be employed a configuration of executing the aforementioned light regulation based on the result of detecting the amount of light irradiating the light valve.
The aforementioned inventions can be advantageously adopted in case the two light sources have different characteristics, but can more advantageously be employed particularly in case the first light source has a period from the turning-on of the power supply to the stable lighting state shorter than that of the second light source. The period from the turning-on of the power supply to the stable lighting state means a period from the timing of turning-on of the power supply to the timing where the light amount reaches 90% of the light amount at a timing after the lapse of sufficient time from the turning-on of the power supply (namely a stationary light emitting state). It is particularly preferable if the period from the turning-on of the power supply to the stable lighting state in the first light source is shorter by at least 15 seconds than that in the second light source.
Also in the aforementioned inventions, there can be advantageously adopted a configuration having a timer for controlling the irradiation of the light valve by the light from the first light source, or a configuration having a light amount sensor for controlling the irradiation of the light valve by the light from the first light source. For example, the light amount irradiating the light valve by the light from the first light source can be controlled according to the output value of the sensor for detecting the output light amount of the second light source.
Also in the aforementioned inventions, there is preferably provided stopping means for stopping the light emission of the second light source for a predetermined period. In this manner, after an interruption of the power supply, the light emission of the second light source can be stopped for the predetermined period. In such case the light valve can be irradiated by the light from the first light source.
The aforementioned first light source can be composed of a xenon-based lamp, a halogen light bulb, a tungsten light bulb, a fluorescent lamp, a light emitting diode or an electron source-based light source, and the second light source can be advantageously composed of a metal halide lamp or a mercury-sealed discharge lamp.
Also in the aforementioned inventions, there is preferably adopted a configuration utilizing, as a filter for filtering the light irradiating the light valve, an optical filter to be employed either of a period in which the light valve is principally irradiated by the first light source and a period in which the light valve is principally irradiated by the second light source.
Also in the aforementioned inventions, there is preferably adopted a configuration having a circuit which executes different operations on the image signal for driving the light valve, respectively in a period in which the light valve is principally irradiated by the first light source and in a period in which the light valve is principally irradiated by the second light source. The aforementioned operation on the image signal can be, for example, an operation of adjusting the contrast, brightness or gamma characteristics of the image.